Process for manufacturing stabilized ceramiclike products from glass by microscopic crystallization



United States Patent 3,227,565 PROCESS FOR MANUFACTURING STABlLIZED CERAMICLIKE PRODUCTS FRDM GLASS BY MICROSCOPIC CRYSTALLIZATION Hideo Tanigawa, 1 7-eh0n1e, Yanagi-dori, Nishinari-ku,

Osaka, Japan, and Hirokiehi Tanalra, Osaka Kogyogijutsushikenjo Ikeda Bunsho-nai 330, Saita-machi, Ikeda, Japan No Drawing. Filed Aug. 8, 1961, Ser. No. 129,980 Claims priority, application Japan, Aug. 13, 1960, 35/34,530 1 Claim. (Cl. 10639) The present invention is concerned with a process for manufacturing ceramiclike products from glass by producing microscopic crystals therein.

As disclosed in the prior art, it is known that ceramiclike products of high strength can be obtained by making glass separate microscopic crystals within the bulk thereof, using as an agent that provides nuclear crystallites or a nucleus-former, so to speak, some metals such as gold, silver and copper or particular sorts of inorganic compounds such as TiO However, such metals as above mentioned are rather expensive, and when TiO is used as a substitute thereof, there is a tendency that the amount of microscopic crystals produced in the glass is restricted within a rather small proportion and at the same time it is necessary to employ such a glass composition as contains a considerable amount of expensive L1 0 as an ingredient, so that'the thus obtained products will become inevitably expensive.

It is, therefore, one object of the present invention to provide a process for manufacturing cerarniclike products from glass by producing microscopic crystals therein. The ceramiclike products are not only producible at moderate prices and in large quantities but also compatible with those of the prior art in respect of the mechanical strength.

It is another object of the present invention to provide a process for manufacturing ceramiclike products from glass by producing microscopic crystals therein on the basis of the discovery of the fact that fluor spar (CaF which is quite inexpensive, is able to be used as nucleusformer not only in the state of crude ore, but with a noticeable advantage of substantial curtailment of the use of costly Li O in the glass composition as raw material.

The present invention is thus concerned with a process for manufacturing ceramiclike products wherein a glass obtained by fusing three constituents of SiO A1 0 and CaF amounting respectively to 4872%, 20-29% and 8-29% by weight together with further additions of M 0 and PhD amounting respectively to 2-7% and 0.2().5% by weight is exposed to a temperature below its softening point but above its transition point to produce nuclear crystallites and then kept at a temperature slightly lower than the softening point of the product to multiply fine crystals thus given rise to.

According to the present invention, a small quantity of PbO is added as stabilizer to the new composition prepared by mixing together finely powdered raw materials of silica (SiO alumina (A1 0 fluor spar (CaF and Li O in the abovementioned ranges of proportion and hence containing Li O which is particularly high in price 3,227,565 Patented Jan. 4, 1966 "ice only in a small proportion. Batches for compositions thus completed were individually melted in a small resistance-heated furnace for 2-3 hours at a temperature of 1,300 C.l,500 C. and the resulting glass was worked by pressing and drawing in the conventional manner to desired form, respectively.

Appropriate samples of each glass were subjected to the following heat treatment. Samples of the glasses were nucleated by beating them in an electrically heated mufiie the temperature of which was uniformly increased at the rate of 300 C. per hour from room temperature until they acquire a temperature below the softening point but above the transition point of the samples, where they were held for l2 hours. The temperature of the mulile was then uniformly raised at C. per hour to 920940, where it was held for 2 hours. In regard to the abovementioned thermal treatment, it may be said that: The first working step of producing nuclear crystallites of CaF can be carried out most efifectively when the shaped glass articles, heated at a speed of 300 C./hr., are kept at a temperature lower by 10 C. than their softening point, as supported by the presence of a CaF deposit confirmed by an X-ray analysis of the glass exhibiting a faint milky turbidity as an implication of the production of nuclear crystallites in this stage of thermal treatment.

The operation for inducing the multiplication of fine crystals in the products can be accomplished most effectively by subjecting the hot products just freed from the mentioned first treatment to a thermal treatment consisting of raising the temperature at a rate of 150 C./hr. followed by keeping the products for 2 hours at a temperature of 920940 C. which is lower by about 50 C. than their softening point, in which final stage of treatment the multiplication of fine crystals is completed. Results of X-ray analysis of the glass distinctly show that the fine crystals deposited in this stage of thermal treatment are of ,B-spodumene and calcium compounds other than CaF indicating that the nuclear crystallites of CaF have become covered with fine crystals of these substances multiplied to such a great extent as makes the pattern of CaF undiscernible at all. As to the possible deformation of shaped articles induced in the course of the thermal treatment, the extent of its occurrence is quite negligible because the change in density can proceed only at a slow rate and in a minute degree.

The abovementioned type of thermal treatment of the abovementioned composition of glass according to the present invention can be very economically performed on account not only because it enables fluor spar (CaF which is obtainable as an ore requiring no special refining and available as a non-expensive agent capable of forming nuclear crystallites, to be directly used as a raw material, but also because it requires neither the use of costly lithium in an amount no more than 27% nor special addition of any material economically incompatible with fluor spar as crystal nuclei producer. The abovementioned economical merits of the method of the present invention are further combined with the advantage that the products obtained thereby are possessed of various virtues as, for example, the smallness in thermal expansibility and the greatness in mechanical strength.

It should be noticed that even the above specified conditions of thermal treatment are only able to give such products as possessed of smaller strengths when they are applied to the compositions made of constituents either NQ e pe 1 1; 19 20 21 22 23 24 above or below the above specified respective ranges of proportion because of the excessive growth of crystal Composition nuclei taking place in that case.

Some of the compositions adopted and the properties 53 so 57 54 51 48 of the products obtained according to the present inveng8 g3 tion will be illustrated in the following table. 5 5 5 5 5 5 1O No. of expernnent 1 2 3 4 5 6 For shaped products before heating Composition Rate of heat expansion per CXlO- 58.6 60.7 68.2 66.5 69.4 72.8 Softening temperature 72 69 6G 63 so 57 C.) 595 590 610 620 625 625 20 20 20 2o 20 8 11 14 17 20 23 5 5 5 5 5 5 For shaped products after heating 0.2 0.2 0.2 0.2 0.2 0.2

Rate of heat erpansion For shaped products before heating per CXlO 12. 0 17. 2 22. 7 26. 1 30. 7 37. 6

20 Flexlon strength (kg/(3111. 950 834 1,313 1,405 1,712 1,802 Rate of heat expansion per CXI0"7 -2 57.1 59. 1 61. 8 65. 4 68. 6 Flexion strength (kgJ cnr 640 023 618 633 603 No. of experiment .2 25 26 27 28 29 30 For shaped products after heating Composition Rate%f1%f0(jpansmn 4 2 6 3 39 per 4 .6 9. 8.5 .4 42.1 Flexion strength (kg. n 0111. .7 1, 715 1,530 2,213 2,228 2, 29s 30 n 14 17 20 23 20 5 5 5 5 5 5 0.2 0.2 0.2 0.2 0.2 0.2

NQ of experiment 7 3 9 10 11 12 For shaped products before heating Com osition Rate of heat expansion p per CX10= 57.7 59.4 61.2 53.5 Softening temperature 54 51 43 9 66 3 C.) 620 605 593 573 20 20 20 23 '23 23 26 29 32 s 11 14 v 5 5 5 5 5 5 For shaped products after heating 0.2 0.2 0.2 0.2 0.2 0.2 40

Rate of heat expansion For shaped products before heating D f C 10- 15.8 1- 5 27. 0 34. 4

Flexion strength (kg./e1n. 804 1,017 Rate of heat expansion per CXIO- 72.5 77.5 82.5 58.2 6110 Softening temperature No. of experiment 31 32 33 For shaped products after heating Composition Rate of heat expansion per 0X1 1 43.9 45.3 48.5 28.4 31.5 sio 54 54 54 Flexion strength (kg./ 26 26 26 No. of experiment 13 14 15 15 17 1s 55 For Shaped products before heating D i Rate of heat expansion per Os non ()-7 8 78 5 Softening temperature C.) 628 595 6g 5:; 5% 5% 4g 66 6O 2 2 2 2 2 26 17 20 23 25 29 8 For shaped products after heating 0 5 5 0 5 5 5 5 .2 2 .2 0.2 0.2 0.2

Rate of heat expansion per (31(10- 56. 8 23. 0 For shaped products before heating FleXloll Strength 250 000 Rate gfhiat e xpansion 9 4 From the data in the table it may generally be ascerg 7 tained as regards the products obtained with the glass C.) 600 613 630 625 620 of the composition specified by the present invention that, While the best result reflected in a low rate of thermal For shaped products after heating 70 expansion as well as in a high flexion strength is obtained in the case of a product prepared by using Li O as added Rate of heat expansion u t 5 e h d ed per CXl0- 35.2 39.5 43.4 44.4 45.2 m an t n of by W a P p epar Wlth maxim strength added L1 0 amounting to 2% by weight shows a value (kg/cm?) 1,460 1,682 1,703 of a rate of heat expansion fairly larger than that shown by that containing Li O of 5% by Weight and a product prepared with added Li O in an amount of 7% by weight gives a smaller value of flexion strength as compared with that containing Li O of 5% by weight. As regards the properties of the glass with the composition specified according to the present invention, it may thus be said that the best result can be obtained when the glass contains Li O in an amount of 5% by weight.

Example Finely powdered raw materials consisting, respectively, of SiO A1 Cal- Li O and PhD were mixed together in the proportions of 54%, 26%, 20%, 5% and 0.2% by weight, respectively (corresponding to the composition in Experiment No. 22 illustrated in the foregoing table). Batches for compositions thus prepared were individually melted in electric resistance-heated furnaces for 2-3 hours at 1,300 C.-1,500 C. and then formed by the routine technique. The rate of thermal expansion and softening temperature of the glass here obtained were estimated as 66.5x- /C. and 620 C., respectively. The above obtained configured article was placed in an electric furnace and heated from room temperature to 610 C. at a rate of 300 C./ hr. and maintained at this temperature for 2 hours. The product thus obtained showed a rate of thermal expansion of 66.5 X 10 C. in accordance with that in the beginning. The product was then heated at a rate of 150 C./hr. and kept for 2 hours at 920 C. The final product thus obtained showed a rate of thermal expansion of 26.1 X 10 C. and a softening temperature of 990 C.

While we have disclosed several embodiments of the present invention, it is to be understood that these embodiments are given by example only and not in a limiting sense, the scope of the present invention being determined by the objects and the claim.

We claim: A process for producing ceramiclike products from glass by microscopic crystallization comprising the steps of heating about 48 to 72% by weight of SiO about 20 to 29% by weight of A1 0 and about 8 to 29% by weight of CaF jointly with about 2 to 7% by weight of Li O and about 0.2 to about 0.5% by weight of PhD for 2-3 hours at a temperature range of about 1,300 C. to 1,500 C. in order to fusesaid material, forming said material into any predetermined shape,

heating said shaped material at a rise of 300 C./hr. to a temperature below the softening point of about 620 C. thereof, yet above the transition point of said glass, to produce nuclear crystallites consisting of CaF and maintaining said material at said last mentioned temperature for about 1-2 hours to efiect the production of nuclear crystallites, then heating the latter at a rate of about C./hr.

to a temperature of 920 C.940 C.,

maintaining said temperature for about 2 hours to produce fine crystallites to be multiplied at said temperature.

References Cited by the Examiner SAMUEL H. BLECH,

JOSEPH REBOLD, JOHN R. SPECK, TOBIAS E.

LEOW, Examiners.

Primary Examiner. 

